This invention relates to a plywood surface defect detecting head of the type used for detecting defects attributable to, for example, knot holes of original plates, worm holes, cracks, and the like, which exist in the surface of plywood.
In the above-mentioned field, it is an actual situation that the afore-mentioned type of defects are confirmed solely by sight of a worker. On the other hand, the applicant of the present invention has proposed in his prior Japanese Patent Application No. 59-188649 a detector for detecting concave-shaped defects in the surface of a plate-like member comprising a shielding member slidingly contacting the surface of a plate-like member at its front end, a moving mechanism for relatively moving the shielding member and the plate-like member, a light source disposed at one side of the shielding member, a number of light receiving elements disposed at the other side of the shielding member with required spaces according to capability of detection and resolution, and a control circuit for detecting the concave-shaped defects in the plate-like member based on light radiated toward the light receiving elements from the light source through a concave-shaped portion in the surface of the plate-like member when the shielding member is positioned in the concave-shaped portion according to the relative movement of the shielding member and the plate-like member.
When detection was carried out depending on a worker's sight, there existed such problems as unstable detection accuracy, poor working efficiency, high costs, etc.
Further, in the Japanese Patent Application No. 59-188649 set forth above, since its constitution is such that a number of light receiving elements are disposed at the other side of the shielding member, and the concave-shaped defects are detected by means of receipt of light passed through the concave-shaped defects by the respective light receiving elements, the light which has passed through the concave-shaped defects is often dispersed before it reaches the respective light receiving elements and enters in light receiving elements adjacent thereto. Accordingly, positions where the concave-shaped defects exist cannot be detected with high accuracy. In addition, light quantity is decreased due to the light dispersion. Because of the foregoing reasons, detection by the respective elements encountered difficulties.
The present invention was accomplished in order to overcome the problems inherent in the prior art.